JPH02278939A - Data decoder - Google Patents

Abstract

PURPOSE:To decode a reception signal in the short time when the state of the transmission line is excellent by varying the length of a path considered to be one path reaching to each state at present in a trellis expressing the state transition of a predictive signal in response to the state of the transmission line. CONSTITUTION:A decoder 6 uses a path selecting signal from a comparator 4, the length of a path considered to be one reaching each state at present in a trellis representing the state transition of a predictive signal is traced back and the decoding of the data at that time is started from the past state by the traced back length. In this case, the decoder 6 changes the length of path considered to be one reaching each state at present in response to the value of a path metric value from a path metric storage device 5. When the state of the transmission line is excellent, the length of the path reaching each state at present to be one is decreased and the decoding of the data at the time traced back by the short length is started, then the quantity of calculation is reduced. The reception signal is decoded in the short time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a data decoding device used in digital mobile communications and the like.

Conventional technology FIG. 2 shows the configuration of a conventional data decoding device.

In FIG. 2, when a received signal is input, the soft decision unit 21
outputs the soft decision value of the received signal at one symbol intervals, and the branch metric calculator 22 calculates the error between this soft decision value and all predicted signals for each symbol.

Next, the adder 23 adds this error to the sum of the branch metrics up to one symbol before (bus metric link) held by the path metric holder 25, calculates the bus metric candidates up to the present, and compares them. The device 24 examines the bus metric links of each candidate and selects the path that gives the path metric with the highest likelihood.

The comparator 24 outputs the selected path metric to the bus metric holder 25 in preparation for calculating a path metric candidate in the next symbol, and outputs a bus select signal indicating the selected path metric to the decoder 26. Using this bus select signal, the decoder 26 traces back a predetermined length that is considered to have a single path leading to each current state in the trellis representing state transitions associated with encoding, and traces the past by the length of the trace. The decoding of data at that time starts from the state of .

Therefore, in the conventional example described above, by tracing back the trellis representing the state transition by a predetermined length, the received signal can be decoded with a certain time delay.

Problems to be Solved by the Invention However, in the conventional data decoding device described above, a received signal is decoded by always going back a predetermined length of a trellis representing a state transition, so if the transmission path is in good condition and the path is short. There is a problem in that even if there is a single signal, there is a certain time delay, and therefore the received signal cannot be decoded in a short time.

SUMMARY OF THE INVENTION In view of the above conventional problems, it is an object of the present invention to provide a data decoding device that can decode a received signal in a short time when the transmission path is in good condition.

Means for Solving the Problems In order to achieve the above object, the present invention determines the state of the transmission line from IJ knock held by a path metric holder, and determines the prediction signal according to the state of the transmission line. In a trellis that represents state transitions, the length of the path leading to each current state is variable and traced back, and decoding of data at that time is started from a past state by the amount of time that has gone back. It is.

Effect of the present invention With the above configuration, when the state of the transmission path is good, in the trellis representing the state transition of the predicted signal, it is assumed that there is only one path leading to each current state, and the length can be shortened. Therefore, the amount of calculation can be reduced, and therefore, when the transmission path is in good condition, the received signal can be decoded in a short time.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a data decoding device according to the present invention.

In FIG. 1, 1 is a soft decision device that outputs soft decision values of the received signal at 1 symbol intervals, and 2 is a one symbol error between the soft decision values determined by soft decision device 1 and all predicted signals. The branch metric calculator 3 that calculates each time adds the error calculated by the branch metric calculator 2 and the sum of the branch metrics up to one symbol before (path metric) held by the path metric holder 5, This is an adder that calculates the path metric candidates up to the present.

4 examines the path metric of each candidate calculated by the adder 3, selects the path that gives the highest likelihood path metric, outputs the selected path metric to the path metric holder 5, and stores the next symbol. This comparator prepares for calculation of path metric candidates in , and outputs a bus select signal indicating the selected path metric to the decoder 6.

Pasta l-IJ knock holder 5 also holds (outputs Smetlinok information to decoder 6, and decoder 6 is held by path metric holder 5) (Sume) IJ
The knock information and the bus select signal from the comparator 4 are used to decode the received signal as described later.

Next, the operation of the above embodiment, particularly the operation of the decoder 6, will be explained.

In FIG. 1, the operations from the soft decision unit 1 to the comparator 4 are the same as in the conventional example, so the explanation of the operations will be omitted.

The decoder 6 uses the path select signal from the comparator 4 to
In the trellis representing the state transition of a predicted signal, the length of the path that is expected to reach each current state is traced back, and decoding of data at that time is started from a past state by the amount of time that has gone back.

Here, since the bus metric held by the path metric holder 5 represents the likelihood of the path, the decoder 6 determines the current value of the bus metric from the bus metric holder 5. Change the length of a single path leading to each state.

In this case, the decoder 6 determines the state of the transmission path when the IJ rack value indicates that the path metric leading to a certain state has a particularly high likelihood. Since it is considered that the path is good and has a high likelihood of being correct, the length of tracing is reduced. On the other hand, when the bus metrics leading to each state are almost equal, the condition of the transmission path is considered to be bad, so the length of tracing is reduced. lengthen.

Therefore, the decoder 6 is the pasta) IJ rack holder 5
If the state of the transmission path is good according to the value of the path metric from Since data decoding is started, the amount of calculation can be reduced, and therefore, the received signal can be decoded in a short time.

As described in detail, the present invention determines the state of a transmission path based on a path metric held by a bus metric holder, and in a trellis that represents a state transition of a predicted signal according to the state of the transmission path. The length of the path leading to each current state is variable, and the length of the path leading to each current state is variable, and the decoding of data at that time is started from the past state by the amount of time that has gone back, so the state of the transmission path is good. In this case, in the trellis representing the state transition of the predicted signal, the length of the path leading to each current state can be shortened, so the amount of calculation can be reduced, and therefore, When the transmission path is in good condition, the received signal can be decoded in a short time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a data decoding device according to the present invention, and FIG. 2 is a block diagram showing a conventional data decoding device. 1... Soft decider, 2... Branch metric operator, 3... Adder, 4... Comparator, 5... Buster)
IJ knock holder, 6... decoder. Figure 1 Name of agent Patent attorney Shigetaka Awano and one other person Figure 2

Claims (1)

[Claims] a soft decision device that outputs a soft decision value of a received signal at intervals of one symbol; a branch metric calculator that computes an error between the soft decision value determined by the soft decision device and all predicted signals for each symbol; an adder that adds the error calculated by the branch metric calculator and the path metric of each path up to one symbol before to calculate path metric candidates up to the present; a comparator that selects a path giving the highest likelihood path metric based on the path metric and outputs the selected path metric and a path select signal; and a path metric holder that holds the path metric selected by the comparator. In the trellis, the state of the transmission path is determined based on the path metric held by the path metric holder, and the path selection signal from the comparator indicates the state transition of the predicted signal according to the state of the transmission path. A data decoding device includes a decoder that traces back by varying the length of a path that is expected to reach each current state, and starts decoding data at that time from a past state corresponding to the length of the path that reaches each current state.